Integration of time-lapse gravity and production data to monitor gas reservoirs

We present a workflow that integrates time-lapse gravity data and production data through a 3D generalized gravity inversion with the objective to monitor water encroachment in a gas reservoir. In this study, we present an analysis of time-lapse gravity and production data acquired in Sebei Gas field in China. Currently, the field is in the late stage of the production plateau. It is therefore important to identify zones of high water flux which may cause a decrease in gas yield. To jointly interpret these two independent data sets, the sparse production data are converted into a reference 3D density contrast model that is subsequently incorporated as a guide into a generalized density inversion. Through this approach, we are able to construct a set of density contrast model, that are consistent with the measured changes in gas/water yield, and whose distribution fits the time-lapse gravity data. The results demonstrate that integrating the production data with the gravity inversion produces an improved definition of density changes from the water encroachment in the reservoir.